1. Field of the Invention
Aspects of the present invention relate to an apparatus for and method of detecting tracking error signals for an optical disc having a high recording density.
2. Description of the Related Art
In general, optical recording and/or reproducing apparatuses to record and/or reproduce data recorded in optical discs such as compact discs (CDs), digital versatile discs (DVDs), High Definition DVDs (HD-DVDs), or Blu-ray discs (BDs) irradiate light onto the optical disc, detect reflected light using an optical detector, and reproduce the data stored in the optical disc using the detected reflection light. In addition, in order to accurately track the optical disc during reproduction of the data, an optical reproducing apparatus detects tracking error signals from the reflected light detected by the optical detector, and compensates for tracking errors using tracking error signals. A differential phase detection (DPD) method is the primary method used to detect tracking error signals.
FIG. 1 is a block diagram showing a conventional tracking error signal detector. Referring to FIG. 1, the tracking error signal detector includes a quadrant optical detector 100, adders 111 and 112, equalizers 121 and 122, slicers 131 and 132, a phase difference detector 140, a subtractor 150, and a low pass filter (LPF) 160. When the quadrant optical detector 100 receives the light reflected by an optical disc (not shown), signals output from regions A and C of the quadrant optical detector 100 and signals output from regions B and D of the quadrant optical detector 100 are respectively added by the adders 111 and 112, and respectively equalized by the equalizers 121 and 122. The slicers 131 and 132 perform a binary coding operation on the signals output from the equalizers 121 and 122.
The phase difference detector 140 detects a phase difference between the binary coded A+C signal output from the slicer 131 and the binary coded B+D signal output from the slicer 132 by comparing the signals with each other. The phase difference detector 140 outputs a phase difference signal PD1 when the phase of the A+C signal leads the phase of the B+D signal, and outputs a phase difference signal PD2 when the phase of the B+D signal leads the phase of the A+C signal. The subtractor 150 detects a difference between the signal PD1 and the signal PD2 (PD1−PD2) output from the phase difference detector 140. The low pass filter (LPF) 160 performs a low pass filtering operation on the difference (PD1−PD2) output from the subtractor 150 to output a tracking error signal.
The optical signal received by the optical detector is sliced for binary-coding in order to compare the phases of the signals. However, if the optical signal includes a part that is not zero-cross sliced, the part is not reflected in the phase difference detection operation.
FIG. 2 shows optical signals S1 and S2 before being sliced and optical signals S1′ and S2′ after being sliced in a case where the optical signals received by the optical detector include parts Z that are not zero-cross sliced. The optical signals S1 and S2 including the parts Z that are not zero-cross sliced are generated by inter-symbol interference (ISI) caused when an optical recording density is increased. The parts Z are not reflected in the binary-coded optical signals S1′ and S2′, and are not used in the detection of the phase difference. The parts Z act as noise that causes a quality degradation of the tracking error signal. Therefore, a solution to solve this problem is required.